Christopher Hogan

Cell therapies hold transformative potential for treating cancer, neurologic disorders, organ failure, diabetes, and other conditions, but their widespread clinical deployment is constrained by the lack of scalable cryopreservation methods that maintain high post-thaw viability. Current standard practice using slow freezing can lead to cell death and impaired cell function. Vitrification offers an alternative by cooling samples rapidly enough to bypass ice formation entirely, better preserving cell structure and function. The high cooling and warming rates required for vitrification have previously been achieved by quenching microliter-scale samples directly into convective cooling and warming baths. Here, we present a cryopreservation platform that overcomes the throughput limitations of existing systems by combining a vibrating orifice aerosol generator with an impinging conical nozzle to generate and confine micrometer-scale droplets mid-flight in liquid nitrogen. This approach mitigates cooling losses due to the inverse Leidenfrost effect, increasing cooling and warming rates by nearly an order of magnitude compared to conventional droplet vitrification, while improving throughput by two orders of magnitude. To test the efficacy of this system, we cryoaerosolized and rewarmed human induced pluripotent stem cells, porcine red blood cells, and human dermal fibroblasts using only 19-25 wt% (2.5-3.7 M) permeating cryoprotective agent, achieving >90% post-thaw viability for HDFs and hiPSCs and 94% recovery for RBCs, with retained colony-forming capacity additionally demonstrated in hiPSCs. This work demonstrates the first scalable vitrification-based cryopreservation method capable of achieving both high cooling (~200,000 K/min) and warming rates (~1,000,000 K/min) while maintaining the high-throughput processing required (>100 mL/h) for next-generation cell therapies.

Understanding particle acceleration in supersonic jet flows is critical in applications including propulsion systems, particle impact modeling, and gas dynamic cold spray deposition. We present velocity measurements of micrometer-sized particles in the [ ] diameter range accelerated through a converging/diverging (CD) nozzle and impinging onto a substrate at speeds approaching [ ] with downstream (preshock) pressures in the [ ] range. Using laser Doppler velocimetry (LDV), we characterize particle velocity distributions across multiple gas compositions (nitrogen, helium, carbon dioxide, and argon) and particle chemistries (ferrous sulfate and ammonium sulfate). We introduce a dimensionless velocity lag to parameterize inertial effects and find that the degree of velocity lag increases monotonically with a modified definition of the particle Stokes number, which accounts for high-speed conditions. Measurement results are compared to particle velocity predictions based upon a three-dimensional simulation of the nozzle flow, with particle trajectories modeled using a recently developed drag model applicable to particles at variable Mach number and Knudsen number. Simulations largely capture the experimentally observed manner in which velocity lag varies with Stokes number.

Final technical report for project Department of Energy - DE-SC0022242. The overarching hypothesis of this project was that the particle dynamics in the afterglow of dusty plasmas are determined by the interplay of the transient plasma properties and the material properties of dust particles. By combining experiments and modeling in an approach fundamentally different from prior research, this project investigated correlations between material properties and basic dust charging and decharging mechanisms.

Complex crater formation is an incompletely understood phenomenon, referring to instances wherein a high-speed projectile impacts a surface and leaves a crater characterized by a central uplift. We elucidate the mechanism of complex crater formation by examining crater formation on different polymer substrates resulting from microparticle impacts with tunable microparticle diameter (1.8 to 6.1 micrometers) and impact velocities up to 840 meters per second. Central uplift is uniquely observed in craters on amorphous polymers, with the degree of complexity directly linked to the polymer thermal properties and homogeneity. We demonstrate that the complex crater volume scales with the ratio of the specific kinetic energy of the impacting object to the specific energy required to raise the impacted substrate to its glass transition temperature (the Eckert number). Our results also confirm that complex crater formation can occur not only for macroscopic celestial collisions but also during sufficiently high velocity collisions at the micrometer scale.